The present invention relates to an arrangement and a method for controlling a compressor of an airconditioning arrangement in a motor vehicle by selective operation of the input to the compressor.
Airconditioning arrangements for motor vehicles are usually driven direct from the engine via a clutch arrangement, which may take the form of a magnetic clutch. Activation of this clutch causes rotation of the compressor""s input shaft and rotary operation of a wobble plate system, thereby causing operation of the compressor""s compressor units.
The environment which prevails in the surroundings of a motor-vehicle-based compressor is arduous in that the compressor is subject to strong vibrations and great heat. As the compressor is driven via a belt, it has to be relatively rigidly fastened to the engine block to avoid belt tensioning problems, and such fastening has the effect of transmitting vibration and heat from the engine block to the compressor. This applies particularly in utility vehicles driven by diesel engines, in which high levels of engine vibration occur. Such vehicles are also often operated under heavy loading on long and frequent runs.
Compressors of airconditioning arrangements for industrial vehicles in particular, such as trucks and buses, are therefore usually affected by operating problems causing a significant service requirement, often including compressor replacement. Operational stoppages are therefore common, and even sometimes total breakdown of the compressor, resulting in irritation for drivers and expense for vehicle owners. Safety risks to the vehicle may also be involved.
One object of the invention is to indicate an arrangement and a method of the kind mentioned in the introduction whereby the problems of the state of the art are obviated or at least reduced. The invention concerns an arrangement and a method for controlling a compressor of an airconditioning arrangement for a motor vehicle, whereby the compressor is optionally driven through activation of a clutch arrangement. The compressor has an input shaft which, via a first wobble plate, acts through bearing elements on a second wobble plate. The second wobble plate is arranged to transmit a wobbling motion designed to drive pistons of a number of compressor units of the piston and cylinder type. A control circuit is designed for brief activation of the clutch arrangement at selected times to cause periodic movement of the bearing elements. The control circuit may be activated by the vehicle starter motor, the reverse gear or a timing circuit.
This object is achieved according to the invention by the features in the characterising parts of patent claims 1 and 6 respectively.
The resulting imposition of a certain amount of movement of the bearing elements between the wobble plates at selected times when the airconditioning arrangement is not being used prevents the bearing between the wobble plates being stationary at the same point for lengthy periods.
Under the state of the art it has in fact been found that running a vehicle with its airconditioning arrangement switched off causes local surface damage in the portions of the compressor""s wobble plates adjacent to the bearing elements, because engine vibrations are imparted to and allowed to act on small surfaces for a long period of time. The invention ensures instead that the bearing elements move somewhat even if the vehicle driver does not activate the airconditioning arrangement, which means that over time the load can be distributed over larger areas of the bearing. The result is longer service life for the bearing and hence for the compressor as a whole. What is also achieved, if movement corresponding to a substantial portion of one revolution of the bearing elements is initiated, is that lubricant present in the compressor housing is propelled around on the moving parts, resulting in better lubrication and longer service life.
The state of the art whereby the wobble plates are stationary if the vehicle driver does not activate the airconditioning arrangement thus means that the engine vibrations transmitted to the compressor have a destructive effect on the wobble plates and bearing elements, entailing disruption of the bearing""s lubricating characteristics and hence impaired bearing function and, ultimately, bearing shearing.
The bearing elements concerned usually consist of xe2x80x9cneedlesxe2x80x9d in the form of cylindrical pins incorporated in a needle bearing between the wobble places. This results in an inherently load-sensitive structure in compressors currently on the market, and consequently major susceptibility of the bearing as a whole to inadequate lubrication. The abovementioned effect on the bearing takes substantially the form of indentations in bearing surfaces, known as fretting or pitting damage, which has been found to seriously impair the bearing""s function and reduce its service life.
On inspection of a compressor that has broken down, it is not at all obvious what has caused the breakdown. Often the bearing elements have melted apart, eliminating all traces of the cause of the damage. Sometimes there has been drastic overheating of the magnetic clutch, causing short-circuiting and even fire in the winding.
It may be noted that previous attempts to achieve longer service life for airconditioning arrangements of vehicles have taken the form of constructional measures such as larger diameters for constituent elements of the compressor. However, such compressors have been substantially more expensive than standard components and have therefore not been economically justifiable in the vehicle industry.
The invention achieves significant advantages such as longer service periods for the airconditioning arrangement (preferably so that they can be matched with ordinary engine service periods), elimination of guarantee work in the form of compressor replacement etc., and less irritation and fewer problems for vehicle users and owners.
Activating the clutch arrangement at the time when the vehicle engine starts up achieves a preferred regular compressor activation. It is also desirable if activation takes place at the time of some other driver action such as reverse gear engagement or the like, but it is also possible for activation to take place without involving the driver at all, e.g. by means of a time circuit set so that activation takes place, for example, once each day or even somewhat more frequently, subject naturally to the vehicle engine being in operation so that driving power can be obtained via the magnetic clutch.
Further advantages are achieved by other aspects of the invention which are indicated below.